1. Field of the Invention
This invention relates to a technique for sewing together two knitted fabric pieces.
More specifically, this invention relates to a method of automatically placing individual knitted loops of two knitted fabric pieces in a position at which they can be sewn together and automatically linking the knitted loops of the two fabric pieces, and an apparatus for implementing the method.
2. Description of the Related Art
Since a knitted fabric is flexible and can be expanded by applying a force to the knitted fabric, so that a dimension of the knitted fabric is easily changed, it is usually impossible to automatically sew together two knitted fabric pieces. Therefore, little progress has been made in automatic sewing techniques and this sewing is still performed by hand using a sewing machine and a proper tool.
More specifically, automation of the linking together of the individual loops of two knitted fabric pieces is very difficult, because it is necessary to position the individual knitted loops of the two knitted fabric pieces together before sewing. Therefore, the linking is usually performed as follows, using a linking machine. Namely, an operator selects each individual knitted loop of a knitted fabric piece and pierces the selected knitted loop with a corresponding piercing needle among a plurality of piercing needles arranged in a fixed frame, and then selects the individual knitted loops of another knitted fabric piece to be sewn together with the first piece and pierces the selected knitted loop with the piercing needle holding the knitted loop of the first knitted fabric piece. The operator then places the plurality of piercing needles holding the two knitted fabric pieces on a linking machine, and the two knitted loops of the two knitted fabric pieces are sewn by using the piercing needles as a guide.
The above-mentioned linking, especially the selecting of individual knitted loops and piercing the selected knitted loops with the piercing needles, is difficult and requires a high degree of skill and good eyesight, and if only one knitted loop among several knitted loops is not selected, the sewn two knitted fabric pieces come apart at the above nonselected knitted loop, and thus the goods produced have a poor quality. Further, since even if linking is performed by a skilled operator it requires much time, this linking work is a great obstruction to any improvement of the labor productivity in a knitted fabric sewing process.
To overcome the above-mentioned drawbacks in the knitted fabric sewing process, several methods of automating the linking have been proposed. For example a method of knitting socks in which a marking thread, e.g., a thread having a color or being a specially finished material different from threads used for knitting the sock and which can be discriminated from the threads for knitting the socks by a reflected ray, is knitted into portions of the socks to be linked, and the piercing work is performed by detecting the marked thread, is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 52-125052. However since it is necessary to previously knit a marked thread into ends of the knitted fabric pieces in this method, this method can be used only when linking portions in a course direction of ends of the knitted fabric pieces, such as toe portions of socks or the like, and this method cannot be used when linking portions of a fully-fashioned sweater, for example, linking two shoulder portions of the bodice or linking the bodice and a sleeve, because the two shoulder portion to be linked and the bodice and the sleeve to be linked have curved edges, and it is difficult to knit the marked thread into those portions.
Further, since the piercing needles are pierced into the two knitted fabric pieces by placing the two knitted fabric pieces on top of each other so that the marked threads are aligned, this method can be used only when the pitch of the knitted loops in the two knitted fabric pieces to be joined is the same and the shapes of the knitted fabric pieces to be joined are symmetrical. Therefore this method cannot be used for linking a front bodice with a back bodice wherein the pitch of the knitted loops is different from that of the front bodice, and the shape thereof is different from that of the front bodice. Consequently, this method is not practical for use on an industrial scale.
A study of a sensor capable of detecting a knitted loop to be pierced and intended for use in automation of the linking is disclosed in IEE PROCEEDINGS Vol 132 No. 4 July 1985, by the Loughborough University of Technology in Great Britain, but this study was limited to the development of a sensor, and there is no publication disclosing an automatic apparatus using this sensor on an industrial scale.